The present invention relates to a de-icing system for de-icing a window pane, in particular a window pane of a motor vehicle.
In vehicles of all kinds there is often during the cold season the problem of the icing of window panes. For example, windscreens of motor vehicles parking overnight in the open air are at freezing temperatures typically coated with a thin ice layer. The manual mechanical removal of this ice layer is tedious and time-consuming, so that in many cases the ice is only removed from a small part of the windscreen before the start of driving. As a result, the visibility is during the first kilometers of driving often substantially limited with corresponding consequences for the active security of the vehicle.
In order to overcome this difficulty it has been known for a long time in the prior art to use systems serving at normal temperatures for cleaning the window pane also for de-icing. Such installations typically comprise a pump spraying a cleaning liquid from a reservoir with one or several nozzles onto the windscreen. The cleaning liquid is provided onto the windscreen with a directed jet from the nozzle, which is only insignificantly influenced by the relative wind, so that the window pane can also be cleaned during driving, and subsequently distributed by operating the windscreen wipers.
In order to additionally de-ice the window pane with such a system, it was suggested to heat the cleaning liquid to an increased temperature so that the ice layer is released and/or thawed, when the hot liquid is sprayed on.
An example of such a device is disclosed in the DE 44 06 653. Here, an isolated container with a resistive heating is arranged in a pipe between the reservoir containing the cleaning liquid and two nozzles. The volume of the isolated container allows a repeated spraying of preheated cleaning liquid onto the window pane of the vehicle.
Apart from the considerable expenditure and the costs caused by mounting the special isolated container, the system according to the DE 44 06 653 puts a load on the battery of the vehicle, since the temperature of the cleaning liquid is constantly kept at an increased temperature. In order to limit the power consumption, the DE 44 06 653 discloses a complicate electric circuitry starting the heating only if the temperature of the cleaning liquid in the isolated container falls below a predetermined temperature. In case of longer standstill times of the vehicle the heating is completely turned off for protecting the battery. Thus, the cleaning liquid cools off overnight in spite of the isolation, so that there is no hot liquid available when the vehicle is started in the morning, but the cleaning liquid must at first be slowly heated in the large isolated container.
A further device for heating the cleaning liquid is disclosed in the U.S. Pat. No. 5,354,965. Here, the amount of cleaning liquid required for each spraying process is heated in a U-shaped heated tube or a small metal container prior to each spraying process in response to pressing a button. After a repeated pressing of the button, the heated liquid is sprayed through a pump onto the window pane. After the end of the spraying process, it is by a suitable arrangement of the metal container with respect to the nozzles and the arrangement of the pipes to the reservoir assured, that the amount of cleaning liquid necessary for the next spraying process remains in the U-shaped tube or the metal container. As a consequence, the installation of this system is difficult, since a reliable operation is only achieved, if the reservoir, the pipes and the U-shaped tube or the metal container are correctly arranged.
Since the metal container or the U-shaped tube are constantly in direct connection with the rest of the assembly, the thermal isolation is comparatively low, so that also here heating times of approximately two minutes are required prior to each xe2x80x9cshotxe2x80x9d.
Heating times of this length are disadvantageous in particular since in both systems according to the DE 44 06 653 and according to the U.S. Pat. No. 5,354,965 a significant de-icing effect is not obtained by a single spraying, even with heated cleaning liquid. The same applies to a further heating system, as it is disclosed in the DE 197 15 359. Since in all of these prior art systems the directed jet of cleaning liquid hits the window pane only in a small part and is to be distributed subsequently by means of the windscreen wipers, at best, only a small part of the window pane thaws, in particular since the window wipers are typically rigidly frozen to the window pane. A quick, de-icing of a large area, which is the precondition for a clear view is not obtained by the systems according to the prior art. Also the repeated application cannot substantially change this, since only the same small part of the window pane is hit by the jet of the heated cleaning liquid.
According to a first aspect, it is the problem of the present invention to provide a de-icing system for a window pane of a vehicle, in particular a motor vehicle, which removes in a short time great parts of an ice layer from the window pane.
According to a further aspect of the present invention, a simple and cost efficient system is to be provided, which heats in a short time the amount of liquid necessary for de-icing and deposits it onto the window pane even after long standstill times of the vehicle, in order to overcome the above mentioned disadvantages of the prior art.
The present invention relates to a de-icing system for de-icing a window pane, in particular a window pane of a motor vehicle with a reservoir for receiving a de-icing liquid, a heating unit for heating the de-icing liquid, a pump pumping the de-icing liquid from the reservoir through the heating unit to at least one outlet, wherein the at least one outlet is shaped such that the heated de-icing liquid is nebulized and precipitates as distributed hot droplets on the window pane to be de-iced.
Thus, the liquid is in contrast to the washing systems from the prior art with an additional heating by the de-icing system according to the invention not deposited in the form of one or more jets directed to the window pane and subsequently distributed by the windscreen wipers but the nebulization according to the invention creates a cloud of dispersed hot droplets above the window pane to be de-iced, which de-ice large areas of the window pane during precipitation. The temperature and the size of the droplets is dimensioned so that their thermal energy is sufficient to respectively thaw a small area of the ice layer. Preferably, the hot droplets have a diameter between 0.5 mm and 1 mm.
Tests have shown, that a single xe2x80x9cshotxe2x80x9d with the de-icing system according to the invention is for temperatures of down to xe2x88x9230xc2x0 C. sufficient to free the major part of a windscreen of a vehicle in a few seconds from the ice. Preferably, the outlet distributes the hot droplets of the de-icing liquid in a fan-shaped manner over the window pane.
In order to shorten in accordance with a further aspect of the present invention, the preparation time for de-icing the window pane in any arbitrary situation, the heating unit heats preferably only the respectively required amount of de-icing liquid for a single nebulization processxe2x80x94preferably directly before the nebulization process. Thus, on the one hand an expensive thermal isolation is not necessary and on the other hand the complex electric circuitries of the prior art for protecting the batteries are nor required.
In a particular preferred embodiment, a first valve is arranged between the reservoir and the heating unit and a second valve is arranged between the heating unit and at least one outlet in order to separate the amount of de-icing liquid necessary for one nebulization process from the remaining de-icing liquid during heating. This improves the thermal isolation of the amount of de-icing liquid necessary for a nebulization process and thus shortens significantly the heating time.
Preferably, the first and second valve are hydraulically opened by starting the pump. Whereas the first valve is preferably provided as a non-return valve, the second valve is preferably provided such that it remains closed against the pressure developing during heating of the de-icing liquid in the heating unit and opens only under an additional pressure increase by starting the pump. Due to the provision and the properties of both valves no requirements concerning the vertical position of the heating unit with respect to the pipes or the reservoir must be, met when the system is installed. On the other hand, expensive electromagnetically controlled valves which are susceptible to trouble are not necessary.
In a particularly preferred embodiment of the present invention the pump starts automatically, if the de-icing liquid arranged in the heating unit has reached a predetermined temperature. Alternatively, the pump can be also automatically started a predetermined time after the beginning of heating.
Further preferred developments are the subject matter of further dependent claims.